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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3941) Unsafe use of DataInput.skipBytes() in StoredPage and StoredFieldHeader
Date Sat, 11 Apr 2009 17:32:14 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12698112#action_12698112
] 

Knut Anders Hatlen commented on DERBY-3941:
-------------------------------------------

Thanks for the patch, Yun!

I have some small comments:

1) skipPersistentDataInput() checks if DataInput.readByte() returns -1 to detect that EOF
has been reached, but I think that that method will throw EOFException and not return -1 on
EOF

2) I think I would have renamed skipPersistentDataInput() and skipFullyDataInput() to skipPersistent()
and skipFully().

> Unsafe use of DataInput.skipBytes() in StoredPage and StoredFieldHeader
> -----------------------------------------------------------------------
>
>                 Key: DERBY-3941
>                 URL: https://issues.apache.org/jira/browse/DERBY-3941
>             Project: Derby
>          Issue Type: Bug
>          Components: Newcomer, Store
>            Reporter: Knut Anders Hatlen
>            Assignee: Yun Lee
>            Priority: Minor
>         Attachments: derby-3941-1.diff, derby-3941-1.stat
>
>
> Some methods in StoredFileHeader and StoredPage call java.io.DataInput.skipBytes(int)
with the assumption that it always skips the requested number of bytes. According to the javadoc
for skipBytes, it may skip fewer bytes than requested, possibly 0, even if the end of the
stream hasn't been reached.
> The problem exists in these methods:
>   StoredFieldHeader.readFieldDataLength()
>   StoredPage.readRecordFromStream()
>   StoredPage.skipField()
>   StoredPage.readOneColumnFromPage()
>   StoredPage.readRecordFromArray()
> We should change the code so that it works correctly even if skipBytes() were to skip
fewer bytes than requested.

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